RX7/B2200 R-Type Gearbox Build

RWD/FWD/4WD it takes all sorts!

RX7/B2200 R-Type Gearbox Build

Postby Fred » Sun Mar 30, 2014 2:33 am

As most of you already know, my truck already has a nice strong gearbox in it. This is a good start in that it doesn't break every time I hit boost or drop the clutch. Yay.

What's not so good is the ratios, they quite literally suck. IIRC shifting at 7500 drops back to about 4k in the next gear, except 5th which drops back to 6800. IE, 12,23,34 are ultra wide and 45 is ultra close. I'd like it more normally spaced for all steps.



Currently I believe the ratios to be:

34/14 * 40/22 = 4.4156:1 first
29/20 * 40/22 = 2.6364:1 second
29/33 * 40/22 = 1.5978:1 third
************ = 1:1 fourth
27/54 * 40/22 = 0.9090:1 recurring fifth

The FD ratios are supposed to be:

3.483:1 first
2.015:1 second
1.391:1 third
1:1 fourth
0.719:1 fifth



Intended solution: FD3S gearbox merged with 12 valve B2200/courier gearbox!

Possible problem: RX input shafts are shorter! :-/ I'm unsure how I'll solve this, but I WILL find a way.



Now for pictures. The first ones are my existing gearbox post cleaning, then the new gearbox as I got it, this morning. Note the truck box is the twisted type and the FD box is the straight type, this shouldn't matter when exchanging internals, I hope. Another possible solution is to get another van bell housing to fit to this and go with a straight style box this time. Who knows what I'll end up doing.



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And the new FD3S batty RX7 gearbox:

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Fred
 
Posts: 190
Joined: Fri Nov 26, 2010 8:19 am

Re: RX7/B2200 R-Type Gearbox Build

Postby Fred » Sun Mar 30, 2014 4:01 am

Fred wrote:Currently I believe the ratios to be:

34/14 * 40/22 = 4.4156:1 first
29/20 * 40/22 = 2.6364:1 second
29/33 * 40/22 = 1.5978:1 third
************ = 1:1 fourth
27/54 * 40/22 = 0.9090:1 recurring fifth

The FD ratios are supposed to be:

3.483:1 first
2.015:1 second
1.391:1 third
1:1 fourth
0.719:1 fifth


Chicken cooker gearbox has the following ratios for 1, 2, 3 with the obvious fourth. I could not confirm reverse or fifth, sadly. That'll come to light during the tear down and swap around. Insides look absolutely mint, barely worn in, definitely not worn out! :-) Such a nice strong design, too. Win.


33/15 * 38/24 = 3.4833*:1 first
28/22 * 38/24 = 2.01515*:1 second
29/33 * 38/24 = 1.391414*:1 third
*************** 1:1 fourth

* in ratio represents recurring

The internet tells the truth! Hopefully fifth is what the inet says, too.

Fred.
Fred
 
Posts: 190
Joined: Fri Nov 26, 2010 8:19 am

Re: RX7/B2200 R-Type Gearbox Build

Postby Fred » Sun Mar 30, 2014 8:07 am

I also measured the input shaft length, but don't have figures on what my truck input shaft is like to compare with, here they are, somewhat rough/inaccurate, for the record, though:

156mm bell housing from face of box to face of engine
158mm from face of box to tip of input shaft
156mm from face of box to usable part of input shaft
127mm from face of box to start of spline
86.5mm from face of box to end of spline

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I can't believe 1st to 2nd will be worse than before! On the other hand, first was useless before and I started in second. That'll change with the 3.9 diff and larger diameter tyres.

Fred.
Fred
 
Posts: 190
Joined: Fri Nov 26, 2010 8:19 am

Re: RX7/B2200 R-Type Gearbox Build

Postby Fred » Sun Mar 30, 2014 8:51 am

Old and new speeds compared:

Image
Fred
 
Posts: 190
Joined: Fri Nov 26, 2010 8:19 am


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